FBE- Uçak ve Uzay Mühendisliği Lisansüstü Programı - Yüksek Lisans

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  • Öge
    Nanosatellite attitude estimation via triad-aided kalman filters
    (Institute of Science and Technology, 2020) Gökçay, Mehmet Asım ; Hacızade, Cengiz ; 634542 ; Department of Aeronautical and Astronautical Engineering
    Increasing demand for the space operations, space industry turns its face to cost effective solutions. Small satellites, due to their size and cost, are receiving interest from many organizations. In 2018, NASA sent two MarCO cubesats to Mars. Their mission was to relay the landing vehicle data back to Earth. Restricted size comes with its own challenges. The amount of attitude determination and control equipment that can be placed in small satellites are considerably lower than a the regular size satellite. In this work, using common sensors, couple of filters are design to overcome to attitute determination problem. Two of most common sensors that are being used in nanosatellites are magnetometers and sun sensors. Magnetic dipole model is selected for magnetic field model. VSOP87 theory is used for sun direction vector. Using these two models, sensor measurement models have been established. For attitude representation of the spacecraft euler angles are selected. Using these angles, equations of motion of the spacecraft are obtained. One of the earliest attitude determination method is algebraic method. Using sun sensor as the first triad, additional two triads have been constructed. Constructed three vectors form a direction cosine matrix. Body angles are obtained from this matrix. In order to increase the accuracy of the satellite motion parameters, three different methods have been analyzed. Extended Kalman filter, unscented Kalman filter and adaptive fading Kalman filters are derived and designed for the system. Comparison of these three filters are studied. Designing the filters, a new sensor type, gyroscopes are used. Measurement model of the gyroscope is obtained. Body angles that are produced by algebraic method are used as linear measurements to the Kalman filters. Hence, two methods are integrated for achieving better accuracy for body angles and angular velocities. Analytic jacobian matrices for EKF have been calculated. Magnetometer and gyroscope biases are estimated. Instead of using magnetometer measurements, magnetometer is corrected with estimated biases. Same process has been applied to the gyroscope measurements. Sensor measurements can be corrupted for many reasons. Aadaptive filters are applied to both EKF and UKF to increases robustness of the both filters. All of the algorithms are designed in MATLAB. Simulation are also conducted at this package program.
  • Öge
    Experimental investigation of a single spanwise vortex gust impinging on a rectangular wing
    (Institute of Science and Technology, 2020) Engin, Kader ; Okşan Çetiner Yıldırım, Nuriye Leman ; 633785 ; Department of Aeronautics and Astronautics Engineering
    The aim of this study is to investigate the effects of a single spanwise vortex impingement on flow structures around and loading on a rectangular wing. An experimental approach is adopted to investigate by gathering force data from the wing and visualization of flow structures with DPIV technic. The experiments are conducted in the large scale water channel located in Trisonic Laboratory of Istanbul Technical University's Faculty of Aeronautics and Astronautics. A Reynolds Number of 10.000 is chosen for all experiments which corresponds to 𝑈∞ = 0.1 m/s. A flat plate upstream of the model undergoing clockwise 180 degree turn is used for the generation of a single vortex and the vortex impacts a stationary rectangular flat plate wing with 𝐴𝑅𝑒𝑓𝑓= 4 located downstream of the vortex generator. Forces acting on the model during experiments are acquired by a force/torque sensor. Simultaneously, flow structures around the wing are captured by a DPIV system during vortex impingement. The mounting arrangements of the gust generator and the wing, are such that both are able to do pitch and plunge motions. A total of 7 different angle of attack values for the stationary wing and 3 different offsets only varying in y-axis for the gust generator with respect to model to change the vortex path are combined to generate 21 test cases of this study. The difference in wing loading due to the vortex impingement for various angle of attack values are compared for the same offset value. Likewise, they are compared when only the gust generator offset changes and angle of attack of the model is kept the same. Following this procedure, images gathered by DPIV system are investigated in conjunction with the force data. The general trend of the aerodynamic forces acting on the model due to vortex impingement shows agreement with the literature work on the subject. Drag coefficient is less affected by the vortex impingement especially when the model has a high angle of attack. However, the lift coefficient shows that asthe angle of attack value increases, the effect of the vortex impingement on lift becomes drastic. The wing loading is correlated with the effective angle of attack calculated quarter chord upstream of the leading edge using the quantitative velocity field obtained using the DPIV system. The study actually mimics a transient vortex gust encounter. The strength and width of the gust is also determined using the DPIV images. Although the impinging vortex is the same for all cases investigated, the offset value and the angle of attack affect the vortex trajectory and therefore wing loading.
  • Öge
    Optimization of design and control parameters for an electrically-propelled aerial vehicle using the energy approach
    (Institute of Science and Technology, 2020) Çiçek, İbrahim ; Nikbay, Melike ; 635569 ; Department of Aeronautical and Astronautical Engineering
    With the recent developments in the aviation industry, the interest in green air transportation has significantly increased over the years. The possibility of green energy sources used in road and rail vehicles could help an alternative option in air transportation as well. After the first development of electrical vehicle concept, Hybrid Electric Vehicles (HEVs) and Battery Electric Vehicles (BEVs) pushed the battery technology to be improved and lead a way to be used for the aerial vehicles as well. The air transport vehicles, considering to be electrified for short-range, regional or urban operations, will depend on energy-based optimization and cost elimination for each flight cycle. The concept of electric aircraft has been studied in recent years because of their innovative appearance and zero carbon emission. Until now, unmanned, vertical or short-range take-off landing, UAV, VTOL/STOL, aerial vehicles are presented for various flight operations. The aerial vehicles powered by electrical energy or driven by e-powertrains are revealed as Electric Airplanes or Electrified Vertical Take-Off Landing Vehicles (e-VTOLs). In this study, the design optimization of the electric air vehicle is presented to develop an approach focusing on the total energy requirement for short-range flights. The developed method is based on the vehicle power consumption for a defined trip/flight profile over a required timespan. Principles of energy requirements during a trip taken into account and the design parameters are estimated. The feasible design proposal is made for short-range flights by suggesting the estimated energy requirement from battery storage. After drawing a rough picture of total energy, the corresponding battery mass, propulsion unit mass, and total vehicle mass is suggested. Since the main energy consumer is the e-motor that generates the propulsion power through powertrain elements, a detail of control parameters optimization is studied for the propulsion unit. In this regard, an online optimization method based on the Optimal Control Theory is proposed for e-motor control parameters. The widely used control method of Proportional-Integral-Derivative (PID) parameters are optimized for the selected e-motor. To come up with the set of optimum PID parameters, the Integral Squared Error (ISE) Method and Interval Halving Search Method (IHSM) are used. All estimations are made with minimum energy requirement consideration. The equations of motions and transfer functions are governed by control and stability equations by introducing the loads exerted on the vehicle. The aerodynamically generated lift and drag, the required e-motor thrust, and total vehicle weight forces during alevel flight are basically implemented.
  • Öge
    A new nonlinear lifting line method for configuration aerodynamics and deep learning based aerodynamic surrogate models
    (Institute of Science and Technology, 2020) Karali, Hasan ; Yükselen, Mahmut Adil ; 638685 ; Department of Astronautics and Aeronautics Engineering
    Determination of the aerodynamic characteristics of unmanned aerial vehicles (UAVs) is of prime importance from both the design optimization and the flight control system design perspectives. Because many of the small, mini, and micro UAV configurations are operated at flight regimes with low Reynolds numbers, the nonlinear aerodynamics and dominant viscous effects play a key role in aerodynamic performance characterization. The existing approaches to determination of the aerodynamic characteristics of small UAVs use either semi-empirical methods with limited prediction capability to reduce computational complexity or computationally intense and complex computational fluid dynamics (CFD) methods. By contrast, in this work, we present a computationally efficient and high-precision nonlinear aerodynamic analysis method for both design optimization and mathematical modeling of small UAVs. First, a new nonlinear lifting line method is developed for lifting surface configurations using Prandtl's classical lifting line theory. This method is further extended to a complete configuration analysis tool that incorporates the effects of basic fuselage geometries. To be specific, the developed method is able to determine the maximum lift coefficient and the pre- and post-stall aerodynamic behavior of a UAV by using its wing and tail section's nonlinear two-dimensional lift curve obtained experimentally or numerically. The method also gives the induced drag directly, and provides the viscous drag and pitching moment coefficients by using two-dimensional airfoil data on the order of 0.01s using a personal computer. A direct comparison between the results of the current method, experiments, and computationally intensive tools shows good agreement. Moreover, we have also developed a deep learning based surrogate model using data generated by our new aerodynamic tool that can characterize the nonlinear aerodynamic performance of UAVs. The major improved feature of this model is that it can predict the aerodynamic properties of UAV configurations by using only geometric parameters without the need for any special input data or pre-process phase. The obtained black-box function can calculate the performance of a UAV over a wide angle of attack range on the order of milliseconds, whereas CFD solutions take several days/weeks in a similar computational environment. The aerodynamic model predictions show an almost 1-1 coincidence with the numerical data even for configurations with different airfoils that are not used in model training. The developed model provides a highly capable aerodynamic solver for design optimization studies as demonstrated through an illustrative profile design example.
  • Öge
    Aerospike nozzle design and analysis
    (Institute of Science and Technology, 2020-07-21) Farrag, Sherif ; Edis, Fırat Oğuz ; 511171132 ; Aeronautical and Astronautical Engineering ; Uçak ve Uzay Mühendisliği
    This research is done to design an aerospike nozzle contour with theory discussion and investigation. Contour is determined using a written Matlab code that gives maximum performance for given conditions. Excel is used to treat the contour points then 3D and 2D model suitable to be imported to Ansys is designed using Solidworks and imported to Ansys Fluent CFD for parameter calculations and analyzing. Truncated Nozzle is analyzed with different percentages, 40% truncation showed maximum performance. Base bleed is added and analyzed. A new conceptual design is first introduced and analyzed in this research "Hybrid Aerospike-Conical Nozzle". It is CFD analyzed and showed a dramatic increase of thrust of 4.6%. Secondary Jets for thrust vector control are added, analyzed and optimized at different positions (20% and 90% measured from the throat). 90% position showed the maximum performance since the amplification factor maximized.